how to make a weapon shatter when hit
The Cell Fracture addon can create sometimes results with parts not cut out. One possible reason for that is non-manifold geometry; as long as mesh will be non-manifold it won't be broken well enough by the addon. You can test that with default monkey (as it's non-manifold because of the eyes):



The areas which have unfinished fractures are ones near the eyes and this is one way to determine where non-manifold geometry is present. Use Ctrl+Alt+Shift+M to make non-manifold parts selected, Mesh Lint addon and others. There are some certain techniques used for repairing such areas listed in the linked answers.